MEMS pressure sensor chips have already extensively been used in the industries of biology, automobile and so on. Generally, a MEMS pressure sensor chip includes a cavity for sensing ambient pressure changes.
In the designs of the prior art MEMS pressure sensor chips, there are mainly two approaches for forming a cavity. The first one is an approach of grinding and the second one is an approach of using a SOI (Silicon on Insulator) wafer.
In the first approach, a groove is first formed in a substrate, and then a bonding layer is formed. The bonding layer can be oxide. The bonding layer can be formed on the substrate, or can be formed on an upper membrane wafer for covering the groove. Then, the upper membrane wafer is bonded onto the substrate via the bonding layer for covering and sealing the groove to form a cavity. Finally, the upper membrane wafer is ground to thin its thickness. In this approach, because of the limitation of grinding processing, the thickness of the membrane formed by the upper membrane wafer is over 10 μm.
The second approach is similar with the first one. The difference lies in that the upper membrane wafer is a SOI wafer. A SOI wafer includes a membrane layer, an insulation layer and an upper silicon layer. After the SOI wafer is bonded to the substrate, the insulation layer is removed to remove the upper silicon layer. A thinner structure can be obtained by using a SOI wafer, but it has a relatively high cost.
Therefore, it is demanded to make an improvement in at least one aspect of the prior art.